Try not to stand next to her ball, because she can cast Dissonance and do damage around it.

938

With proper reaction speed, you can Flash away from Orianna's ultimate.

821

Although both Orianna's auto attacks and spells do massive damage, she is very fragile. Try focusing her in teamfights.

756

Orianna's ball, when on the field, has most mobility moving from side to side, as she can move it with less range requirement. to avoid being hit by the ball so much, try staying behind it (ball in front of you). this way she must come closer to hit you.